It is typically the case for passenger trains that all of the wagons of the train have the same origin and end destination. Even at the end destination, it is rarely the case that disassembling of the wagons, except for probably the end wagons, is done. In contrast, freight trains are better thought of as a temporary grouping of wagons coming from different origins and going to different end destinations. In accordance with the logistics planned for the cargo that they transport, freight trains are assembled and disassembled in locations called shunting yards. Thus, any given wagon may be part of different freight trains during its journey from its origin to its end destination.
In the shunting yards, the assembling of trains is done using appropriate algorithms such that all of the wagons in the train have the same next hop and that wagons with closer deadlines for their end destinations are put before those with longer ones. This scenario is, however, a simplification since also to be taken into account are factors such as, for example, the availability and the number of turning tables at the shunting yard, the space available for the disassembling/assembling and the time slots allocated for such purposes for any given train, etc. Currently, decisions on how to best satisfy all such conditions is made locally by staff at shunting yards. Thus, whilst a freight train may be assembled such that all the wagons of the train have the same next hop, it is usually not possible to compile them in accordance with the timetable of their respective end-destinations, i.e. that wagons with closer deadlines to their end destinations are placed before those with later ones may not be achieved.
When a freight train arrives in the next shunting yard, the structure of the train should be known before it is disassembled and before its associated wagons are assembled into other freight trains. A course of action for achieving this may be that the staff responsible for assembling the train record the order of its wagon compilation before the train leaves and transmit this information to the next shunting yard. However, this may not always be feasible since assembling of the trains is typically done in parallel and in an optimistic fashion with staff at the shunting yards applying local decisions as to the wagon order. A further reason why this is not done is because wagons may be added or removed outside of the shunting yard from and to the back of the train or even in the middle.
The problems associated to the manual assembling and disassembling of freight trains is further exacerbated by the fact that such trains are typically very long, for example, in the United States, freight trains may contain hundreds of wagons and may span over several kilometers.
Attempts have been made to use radio frequency identification (RFID) technology to identify wagons and thereby determine the composition of a train. However, problems due to RFID tags getting lost or deteriorated due to the extreme environmental conditions that the train may be exposed to during its journey has meant that these attempts have not always been successful.
Accordingly, it is a challenge to determine if and how the order of wagons in a train, particularly a freight train, is changed in a more reliable manner than is presently the case.